Significance Evidence from animal studies and from brain damaged human subjects indicates that certain brain regions such as the amygdala, the temporal polar cortex and the orbitofrontal cortex play essential roles in the orchestration of social behavior. Understanding these neural systems will have implications for understanding normal social behavior, for understanding, treating and ultimately preventing neurodevelopmental social disorders such as autism and societal concerns such as psychopathology and criminality. Objectives Studies under way are investigating the role of the amygdala in dyadic and tetradic social interactions between macaque monkeys. Highly specific lesions are produced in the amygdala and alterations of social function are observed and quantified by using computer assisted behavioral analysis. Results We have recently completed a 2 1/2 year intensive study of six monkeys with bilateral amygdala damage and 6 age, sex and dominance matched controls. Not only do animals with amygdala lesions demonstrate abnormal interactions with inanimate objects (they lack a normal reluctance to engage a novel potentially threatening object) but their social interactions are altered as well. A novel finding is that the normal animal rapidly detects a difference in the amygdala lesioned animals and demonstrates more affiliative behaviors towards them. Future Directions A second cohort of animals for total amygdala lesions is currently under selection. These animals will be used for refined analysis of social interaction. Preparations are currently under way to initiate funded studies of the effects of neonatal amygdala disconnection on the emergence of social behavior. Finally, the effects of amygdala lesions will be investigated on the ability of macaque monkeys to discriminate facial expressions. KEY WORDS amygdala, social behavior FUNDING NIH Grant MH/HD57502